Polyphosphate detergent compositions containing dicyandiamide tarnish inhibitor



POLYPHOSPHATE DETERGENT COMPOSITIONS COfiAlNING DICYANDIAMIDE TARNISH IN- IIB OR Charles E. Light, Damien, Conn, assignor to American Cyanamid Company, New York, N.Y., a corporation of Maine No Drawing. Filed Nov. 15, 1954, Ser. No. 469,001

2 Claims. (Cl. 252137) This invention relates to compositions and methods for inhibiting the formation of discoloration or tarnish on metal surfaces caused by the action of certain watersoluble salts when said salts are used alone as cleansers or in combination with soaps and wetting agents.

It is known that certain water-soluble inorganic polyphosphates have the undesirable property of causing some metals to become discolored and tarnished. This is particularly noticeable in the household where kitchenware such as cutlery and kitchen utensils are exposed to repeated washings by compositions containing these salts or by cleansers and water softeners containing these salts alone. With the trend toward modernizing kitchens, more metal surfaces are being provided in the form of drain boards, shelving and trim. With the increased use of wetting agents containing tarnish-forming salts as household cleansers, the matter of maintaining metal surfaces untarnished in appearance with a minimum of effort, has become one which requires considerable attention because of the discoloration caused by these household cleaning agents. I

Many household cleansers are merely mixtures of common organic wetting agents, certain water-soluble inorganic polyphosphates and other ingredients. The polyphosphates are often used alone as cleansers, watersofteners and for other purposes but most often they are used with detergents other than polyphosphates and wetting agents. coloration and tarnish is due largely to the exposure of the metal surfaces to the action of the water-soluble inorganic polyphosphates rather than due to atmospheric oxygen. The exposure may be in the form of numerous washings, as in the household and kitchen utensils, or it may be in the form of prolonged soaking in solutions containing the tarnish-forming water-soluble inorganic polyphosphates. The discoloration is usually in the form of a brown tarnish that cannot be easily removed.

In the household cleansers previously mentioned the principal active ingredients are a wetting agent and a water-soluble inorganic polyphosphate in quantities on the order of 15 to 35 and 5 to 50 parts by weight respectively. In addition, they may contain other ingredients in varying amounts such as sodium sulfate (9-24 parts), sodium carbonate (1 to 20 parts), sodium chloride (up to 4 parts), sodium silicate (3 to 10 parts), magnesium sulfate (about 5 parts) and starch (about 15 parts). These additional ingredients are not essential to the composition since any or all of them may be eliminated but they contribute to the production of a commercially acceptable household cleaning composition. The use of a detergent or wetting agent is also optional, but such organic wetting agents are almost always present in the commercial cleaners used for washing knives and forks, Monel metal, German silver and other copper-containing metals.

The water-soluble inorganic polyphosphates referred to are the so-called calcium-sequestering polyphosphates. The term calcium-sequestering polyphosin either case, it is known that the dis- 2,967,832 Patented Jan. 10, 1961 phates is meant to include those phosphates which prevent calcium ions and other polyvalent metal ions,v

such as magnesium, from precipitating in aqueous solution. It is believed that this is accomplished by the formation of soluble complexes of such metal-containing phosphate ions. These calcium-sequestering phosphates are usually employed as alkali metal salts of which the following are representative: tetrasodium pyrophosphate, pentasodium triphosphate, sodium hexametaphosphate and hexasodium tetraphosphate as well as various corresponding acid salts such as disodium dihydrogen pyrophosphate, and other soluble salts of basic ions such as pentapotassium triphosphate. All such calcium-sequestering phosphates have a plurality of phosphorous atoms and are referred to in this specification as polyphosphates.

Efforts have been made to prevent the tarnishing that occurs when copper-containing metal surfaces are washed with synthetic detergent compositions; however, these efforts have frequently been unsatisfactory. I believe that many such failures have been caused by the mistaken belief that the tarnish is due to the action of the water-soluble sulfur-containing wetting agents in the detergent compositions, instead of the polyphosphates which these compositions always contain. Moreover, even in the few cases where the tarnshing action of polyphosphates has been recognized, the inhibitors proposed have been quite expensive.

It is another object of this invention to provide a composition wherein the discoloring action of polyphosphates on metal surfaces, particularly coppery metals, is reduced or inhibited by the presence of a novel low cost discoloration inhibitor.

It is still another object of this invention to provide an ingredient of a composition for reducing or inhibiting the formation of tarnish due to the action of watersoluble polyphosphates when they are used as cleansers.

it is yet another object of this invention to reduce or inhibit the formation of tarnish on metal surfaces caused by the action of polyphosphates when they are used in admixture with soaps and wetting agents.

It is another object of this invention to provide a method for washing copper-containing metals so as to reduce or inhibit the formation of tarnish on the metal surface by the action of water-soluble polyphosphates.

Other objects will appear as the description of the invention is continued.

It has now been found that the discoloration and tarnish formation on metal surfaces caused by watersoluble polyphosphates in detergent solutions therefor is reduced or inhibited by the presence therein of tarnish inhibiting amounts of dicyandiamide.

I have found that dicyandiamide is highly effective while on the other hand free guanidine, guanylurea and biguanide are lessstable and not as effective after a long period in hot water.

It is found that amounts of the inhibitor in the order of .01 to 2% of the dicyandiamide based on the weight of the polyphosphate is effective and adequate. The use of inhibitor in excess of 2% is seldom desirable since the increase in tarnish-inhibiting effect is not proportionally increased.

The discoloration inhibitor of this invention is effective against the tarnish forming polyphosphates irrespective of the quantity or type of soap or wetting agent used. Therefore, any desired quantity of any soap or wetting agent may be used in conjunction with the tarnish form ing polyphosphates and the discoloration inhibitor of this invention. Among the soaps and wetting agents commonly used are the alkyl sulfates of aliphatic alcohols of 814 carbon atoms, alkylaryl sulfonates and particularly the alkylbenzenesulfonates containing alkyl radicals of openness -l2 carbon atoms, sulfonated esters such as sodium dioctyl sulfosuccinate, condensation products of ethylene oxide and higher alcohols of 8-18 carbon atoms and condensation products of ethylene oxide and higher fatty acids of 8-18 carbon atoms and acid mixtures.

Wherever the polyphosphates are the cause of discoloration on metal surfaces, the inhibitor of this invention may be effectively used to reduce or inhibit such discoloration. Therefore, it will be seen that this invention is not specific to any single class of metals or alloys. Among the metals and alloys that are normally discolored by the polyphosphates, the non-ferrous coppery metals and alloys thereof such as copper, German silver, brass, various other alloys of copper and copper that has been imperfectly plated with metals such as silver, nickel and chromium are notable.

The following tables will illustrate the eifectiveness of the discoloration inhibitor of this invention. In the tables the percent of the discoloration inhibitor added is based on the Weight of the polyphosphate. The Ultrawet SK referred to in the Tables I and III is an alkyl-aryl sulfonate detergent obtained by condensing tetrapropylene with benzene to make dodecyl benzene and then sulfonating it. The product contains 35% by Weight of dodecylbenzenesulfonate and 65% sodium sulfate and is a spray dried product.

1 In contact with strips of German silver.

The number 1 indicates no visible tarnish. The numbers 2, 3 and 4 indicate increasing amounts of tarnish. The number 5 indicates a heavy brown discoloration.

TABLE II Tamish development [05% dioyandlamide added] Composition 1 7 min. min. 30 min.

Sodium Tripolyphosphate 1 2+ 3+ Tetrasodium pyrophosph e 1 2+ 3+ Sodium Hexametaphosphate- 1 2 3 Pentasodium phosphate 1 2+ 3 Hexasodlumtetraphosphate 1 2 4 1 0.17% aqueous solution of the polyphosphate with .057, dieyandiani ide added based on the weight of the phosphate in contact with strips of German silver.

4 TABLE 111 Tarnish development [2% dicyandiamide added. based on the weight of the polyphosphaie] Composition 1 7 min. 15 min. 30 min.

Sodium Tripolyphosphate 1 1+ 2 Tetrasodium pyrophosphate. 1 2 8 Sodium Hexametaphosphate 1 l 2 Pentametatetraphosphate. 1 2 3 TTt-Kametatetraphosphate 1 2 1i Ultrawet SK 30.0

Sodium tripolyphosphate 45.0

Balance (sodium sulfate, sodium carbonate, sodium silicates) 25.0

Dicyandiamide in a quantity of 0.4% on the weight of the sodium tripolyphosphate was added to an 0.1% aqueous solution of this composition. Strips of German silver were suspended in the resulting solution for 30 minutes. No tarnish was visible after this time.

Having thus described my invention, I claim:

1. A detergent composition suitable for use in washing copper-containing metals comprising from about 15 to 35 parts by weight of an organic detergent, about 5 to 50 parts of an inorganic alkali metal polyphosphate normally causing tarnishing of said copper-containing metal and, as a tarnish-inhibitor for said polyphosphate, from 0.01 to about 2 parts by weight of dicyandiarnide.

2. A method of washing copper-containing metal While avoiding the tarnishing thereof which comprises applying to said metal a dilute aqueous solution of a detergent composition containing an inorganic alkali metal polyphosphate normally causing tarnishing thereof and also containing 0.01% to 2% of dicyandiamide on the weight of said polyphosphate to inhibit its tarnishing action on said copper-containing metal.

References Cited in the file of this patent UNITED STATES PATENTS 2,280,995 Booth Apr. 28, 1942 2,445,975 Shepard July 27, 1948 2,535,972 Vitalis Dec. 26, 1950 2,706,179 Tundermann Apr. 12, 1955 FOREIGN PATENTS 510,621 Belgium Oct. 11, 1952 ATENT OFFICE F CORRECTION January 10, 1961 CERTIFICATION 0 Patent No. 2,967,832

Charles E. Light It is hereby certified that error appears in t ent requiring correction and that th corrected below he above 11 e said Letters umbered pat- Patent sho uld read as SEA L) Attest:

ERNEST W. SWIDER Commissioner of Patents 

1. A DETERGENT COMPOSITION SUITABLE FOR USE IN WASHING COPPER-CONTAINING METALS COMPRISING FROM ABOUT 15 TO 35 PARTS BY WEIGHT OF AN ORGANIC DETERGENT, ABOUT 5 TO 50 PARTS OF AN INORGANIC ALKALI METAL POLYPHOSPHATE NORMALLY CAUSING TARNISHING OF SAID COPPER-CONTAINING METAL AND, AS A TARNISH-INHIBITOR FOR SAID POLYPHOSPHATE, FROM 0.01 TO ABOUT 2 PARTS BY WEIGHT OF DICYANDIAMIDE. 